Method for the production of acrylonitrile composite fibers



United States Patent U.S. (1264-168 2 Claims ABSTRACT OF DISCLOSURE A method of manufacturing helically crimped composite fibers of the acrylonitrile type, comprising concurrently extruding two'or more spinning solutions of the same-polymer but having different concentrations of the polymer therein to form a bicomponent fiber, washing and stretching the resulting gel fiber, then drying the resulting fiber under relaxed conditions at temperatures below 80. C. and steaming the crimped fiber in a relaxed and confined state at a temperature of at least 110 C.

This invention relates to a method of manufacturing a composite fiber of the acrylonitrile type which possesses an excellent three-dimensional coil crimp which is resistant to heat and is sufiiciently durable.

It is conventional practice to impart a crimp to a textile fiber by mechanically bending it. More recently a composite fiber has been developed which is capable of developing an improved crimp, said composite fiber consisting of two or more dissimilar polymer. components which differ from one another in thermal behavior as arranged eccentrically along the entire length of said fiber.

However, the former method involves a mechanical treatment, employing, for instance, a stuffing box which could damage the fiber; in addition to which the crimp so developed is not sufficiently durable, nor it is resistant to heat. As regards the latter method, since at least two dissimilar polymers areemployed, the components of the resulting fiber might become separated, resulting in a serious breakdown of the fiber, or uneven dyeing may result owing to the presence of dissimilar compositions of said polymers constituting the fiber. I

The present invention provides means for producing a composite fiber possessing an excellent crimp comparable to that of the conventional composite fiber and yet free from the above-mentioned disadavntages, said means comprising the employment of two or more spinning solutions which differ from each other in polymer concentration but are prepared from the same type of polymer.

Whereas the conventional composite fiber gives rise to a crimp due to the difference in thermal shrinkage of its two or more different polymer components, the present invention gives effective crimps, due to specific processing of fibers made from dopes having different concentrates of the same polymer.

A water-soaked swollen fiber, in gel state, is obtained when a spinning dope of a polymer composed predominantly of acrylonitrile as defined herein below, is coagulated in an aqueous bath. It remains swollen even after passing through washing and hot-stretching steps, but since the degree of swelling primarily depends on the concentration of the polymer in the spinning solutions extruded, a coil crimp is obtained due to the difference in swelling of the components if a composite fiber made up of two or more solutions of a single polymer which have different degrees of swelling potential is dried under 3,463,846 Patented Aug. 26, 1969 "ice no tension. The present invention is based on this novel finding.

The degree of swelling of gel fiber extruded through a spinnerette not only depends on the polymer concentration of spinning solutions but it also is affected by the composition and temperature of the coagulating bath and the washing water, the temperature at which the fiber is stretched, as well as the temperature in other steps where the fiber is heated. It is, therefore, rather easy to change the degree of swelling of fiber in the spinning process, but it is not easy to create certain local differences in swelling in each of the gel fibers processed uniformly. In order to secure a sufiicient crimping effect, which is of any practical importance, according to this invention, it

is preferred that the difference in the polymer concen- ,tration of the two or more different spinning solutions of the same polymer be greater than 2 percent.

Since, as aforesaid, the degree of swelling of a moistureladen gel fiber is substantially affected by heat in the spinning process, it is necessary to select such spinning conditions as would not diminish the difference in the degree of swelling between the components constituting the gel fiber.

Thus, it has been found that in the step of drying or compacting an acrylonitrile gel fiber consisting of two or more components having different degrees of swelling after hot-stretching, said fiber must be subjected to a temperature below C. in a relaxed state in order that three-dimensional coil crimps may be efficiently developed due to a difference in shrinkage of the components of the fiber while drying, said difference in shrinkage, in turn,

being derived from said difference in swelling of the fiber components. If the gel fiber is dried or compacted at any temperature above 80 C., the thermal shrinkage of the fiber will be too great and diminish the difference in the shrinkage between its components, thereby adversely affecting the development of a three-dimensional crimp. Furthermore, it is necessary to keep each of the filaments unrestrained by one another and free to move during said drying or compacting step in order to ensure effective development of three-dimensional crimps.

The composite fiber which has had its coil-crimping potential fully achieved in the drying or compacting process is then treated with steam whereby said threedimensional crimp is set and, at the same time, the fiber is relaxed. However, since the composite fiber of this invention is intrinsically made up of a single type of poly crimps in the course of said heat treatment in relaxedv state, it is necessary to provide a mechanical device whereby not only may the filaments be held under no tension but coil crimps developed already may hold their shapes by restraint due to friction and other physi-. 7

cal forces. This may be achieved by allowing the fiber which has had its coil crimp developed in the course of said drying or compacting process to drop in folds in the bottom of a container made up preferably of wire netting or perforated plate-s, as for instance, in such a manner that the fiber is arranged in many parallel lengths, and, then, the container is closed with a cover which is also made up of wire netting or perforated plates. In this step, it is preferred that the fiber is arranged in the container at a density of from about 0.2 g./cm. to 0.005 g./cm. The container is then tilted by degrees so that the parallel lengths of fiber are also parallel with the direction of gravity, in which state the tension forces acting on the monofilaments are minimized. The fiber, in this-relaxed state, is heat-treated in steam, whereby the three-dimensional coil crimp is perpetuated and, at the same time, the effect of relaxation heat-treatment is obtained-To attain this dual purpose, the steam treatment must be carried out at temperatures of at least 110 C.

The'crimp of the composite fiber of this invention which emerges from such a crimp-setting and relaxation heat-treatment is extremely resistant to heat and if this composite fiber is drawn until its coil crimp disappears and, then, is immersed in hot water, the coil crimp is immediately regained. It is obvious that the composite fiberofthis invention has a three-dimensional coil crimp which is superior to the conventional mechanical crimp in both bulkiness and feeling.

Because the composite fiber of this invention is intrinsically made up of a single type of polymer, there is encountered neither uneven dyeing nor splitting of the components, the characteristic phenomena of the composite fiber consisting of dissimilar polymers.

The term polymers of the acrylonitrile type as used throughout this specification means the polymers composed mainly of acrylonitrile, inclusive of the copolymers between acrylontrile and other vinyl monomers copolymerizable therewith, as well as the mixed polymers with other polymers. The other vinyl monomers and other compounds copolymerizable with acrylonitrile include, for example, vinyl acetate, vinyl chloride, vinylidene chloride, acrylic acid, methacrylic acid, and other acrylic acid derivatives, acrylamide N-methylolacrylamide and its related derivatives, vinyl pyridine and its derivatives, allylsulfonic acid, methallylsulfonic acid and its derivatives, as well as all other monomers copolymerizable with acrylonitrile.

The method of this invention is particularly useful when applied to cases in which a polymer of the acrylonitrile type is dissolved in a solvent such as aqueous solu tions of sodium thiocyanate, nitric acid, zinc chloride, dimethylformamide, or dimethylsulfoxide, and the resulting spinning solution is wet-spun using an aqueous coagulating bath.

This invention will be further described in detail by way of the following example, in which all percents are by weight.

EXAMPLE A copolymer consisting of 90% acrylonitrile, 9.5% methylacrylate, and 0.5% sodium methallylsulfonate is dissolved in 49% aqueous solutions of sodium thiocyanate to prepare two kinds of spinning dopes, the copolymer concentration of which are 8.5% and 11%. Equal parts of the dopes are extruded through an extrusion apparatus, with which two metering pumps are connected, in 10% aqueous solution of sodium thiocyanate at C. The resulting fiber is washed with water at 30 C. and then stretched in boiling water to 9 times its initial length. The spinnerette used in this example has 6532 orifices, each measuring 0.09 mm. in diameter. Tows of this fiber are then dried in hot air streams at 40 C., 60 C., 80 C., 100 C., and 120 C., respectively, under no tension for 60 minutes.

These samples are allowed to fall in parallel folds into a container of perforated plates, 20 cm. x 20 cm., in such a manner that each fold of the fiber measures about 20 cm. and the density of the fiber is about 0.05 g./cm. The container is closed with a perforated cover and, then, tilted by 90 degrees. In this state, the fiber is subjected to a crimp-setting and relaxed heat-treatment in saturated water vapor at 125 C. for 10 minutes.

The degree of crimping of each of the samples is measured according to I IS L1074. The results were summarized in Table 1.

As shown in Table 1, there is substantially no .crimp obtained when the fiber is dried at 100 C., or higher. The monofilaments of the samples which have been'dried at 40 C., 60 C., and C., respectively and, then, treated with water vapor as above ,are stretched 20% in hot water at C. and at room temperature until the crimps disappear completely. Then, as the monofilaments are immersed in hot water at 95 C. in a relaxed state, the three-dimensional coil crimps are completely regained. On the other hand, when the samples dried under no tension in hot air streams at 40 C., 60 C., and 80 C., respectively, are packed into a perforated container as above and are treated without being tilted by 90 degrees with saturated water vapor at 125 C. for 10 minutes, there apparently is some local disappearance of crimp in the fiber.

What we claim is:

1. A method of manufacturing a helically crimped composite fiber of the acrylonitrile type, characterized by the steps of concurrently extruding two or more spinning solutions of the same polymer but having different concentrations of said polymer therein to form a bicomponent fiber, washing and stretching the resulting gel fiber, then drying the same under relaxed conditions at temperatures below 80 C. to develop coil crimps in the fiber, folding the thus-formed crimped fiber in a container so that the resulting folds of fibers lie in layers in a horizontal plane in a relaxed and confined state and at a density of from about 0.2 gm./cm. to 0.005 gnr/cm. and turning the container at an angle of 90 so that the fibers lie in a longitudinal plane and are parallel to each other, and then steaming the folds of fibers at a temperature of at least C.

2. The method according to claim 1 wherein the difference in concentration of polymer between the two or more spinning solutions is greater than about 2%.

References Cited UNITED STATES PATENTS 2,439,815 4/1945 Sisson 264-171 X 2,987,797 6/1961 Breen.

3,038,240 6/ 1962 Kovarik.

3,039,524 6/1962 Belk et al.

3,052,512 9/1962 Kocay et al.

3,084,993 4/1963 Dawson et al.

3,111,366 11/1963 Fujita et al.

3,316,611 5/1967 Terra et al. I 264-168 X 3,330,896 7/1967 Fujita et al 264l03 3,339,250 9/1967 Comolli et al. 264168 3,363,041 1/1968 Schichman et al. 264l68 X FOREIGN PATENTS 1,382,834 11/1964 France.

JULIUS FROME, Primary Examiner J. H. WOO, Assistant Examiner US. Cl. X.R. 1

286Z, 72; 264l7l, l82, 234,342 

